str.word_iter().collect() allows slices to escape the borrowck

[huonw]

fn main() {
    let v = {
        let s = ~"foo bar";
        s.word_iter().collect::<~[&str]>()
    };
    println(v.to_str());
}
// prints [foo, , ^@]

Changing the v.to_str() to fmt!("%?", v) still compiles and outputs

rust: task failed at 'left: 0 does not equal right: 128', /home/huon/rust/src/libstd/str.rs:1727
rust: domain main @0x25ba1b0 root task failed

[nikomatsakis]

Investigating.

[nikomatsakis]

I believe this is due to #5781

[huonw]

This appears to be fixed:

<anon>:5:28: 5:29 error: borrowed value does not live long enough
<anon>:5         let s = ~"foo bar"; s.word_iter().collect::<~[&str]>()
                                     ^
<anon>:3:10: 8:1 note: borrowed pointer must be valid for the block at 3:10...
<anon>:3 fn main() {
<anon>:4     let r = {
<anon>:5         let s = ~"foo bar"; s.word_iter().collect::<~[&str]>()
<anon>:6     };
<anon>:7     println(fmt!("%?", r))
<anon>:8 }
<anon>:4:12: 6:5 note: ...but borrowed value is only valid for the block at 4:12
<anon>:4     let r = {
<anon>:5         let s = ~"foo bar"; s.word_iter().collect::<~[&str]>()
<anon>:6     };
error: aborting due to previous error
application terminated with error code 101

But I'm not sure why: @nikomatsakis do you know of anything that would've fixed this?

[emberian]

This does compile now, and outputs [[oo, , r]

[nikomatsakis]

I still suspect the error is #5781. If I find the time, I'll probe a bit more deeply this week.

[alexcrichton]

Closing, this compiles with a correct error now:

fn main() {
    let v = {
        let s = "foo bar".to_string();
        s.as_slice().words().collect::<Vec<&str>>()
    };
    println!("{}", v.to_string());
}

Additionally, the cc'd issue #5781, is closed, so I believe the relevant tests are all checked in.